People keep saying "read the tooltips", but there's information that is just not there, namely the fact that the combo steps that make sense to use at any given time will be highlighted. For the basic combo it means the only actual decision you need to make is whether to refresh the debuff on your target or not.

I found the official job guide a lot more useful than the in-game tooltips: https://na.finalfantasyxiv.com/jobguide/viper/

Because it summarize a lot of things with diagrams.